Long rod kinetic energy penetrators are used in ordnance in various calibers from 25 mm to 120 mm. In all cases, these penetrators require a sabot assembly to impart kinetic energy and momentum to the sub-caliber kinetic energy rod while being launched from the gun. The sabot assembly must effectively disengage from the rod once it has left the gun so as not to excessively degrade the kinetic energy of the penetrator in its flight to the target. It must also be constructed of high strength light weight material so as to minimize its parasitic weight.
At the present time, a typical sabot assembly is composed of matched sections, usually three or more, that engages the grooves on the penetrator rod. During launch, while the assembly and rod are traveling in the gun barrel, the propellant gas pressure and the rotating band engraving operation for rifled gun barrels maintain the sabot assembly on the rod so that the accelerating forces on the sabot can be transmitted effectively to the rod and accelerate both the sabot and the rod together down the gun barrel. Once the sabot and rod are out of the barrel, aerodynamic forces are used to lift the sabot sections free of the traveling rod. This disengagement is critical, since it must be done so as not to give any extraneous moment of force to the rod which would cause the rod to deviate off target. The sabot is designed to provide an air scoop in the front of the sabot and this air scoop must provide sufficient disengagement force. As is often the situation, effective disengagement is difficult to achieve reliably without somewhat affecting the flight accuracy.
The kinematics of sabot removal is complex and involves conservation of momentum and force and moment interactions between the sabot sections and the penetrator rod to which they are attached. Kinematically, a clean sabot discard requires the forces on the penetrator rod to be balanced at the instant of separation so as not to impart an overturning moment to the penetrator projectile.